Image sensing apparatus and its control method

ABSTRACT

A drive mode is switched after readout for one frame is completed, and the reset operation for the following frame is started. In this manner, the reset operation for the following frame will not be performed during the readout period for the preceding frame. Therefore, the accumulation period for the following frame can be made consistent in that frame.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image sensing apparatus and itscontrol method.

2. Description of the Related Art

An exemplary mechanism for electronic zoom processing in CCD cameras isshown in FIG. 1. In FIG. 1, reference numeral 100 denotes a lens,reference numeral 101 denotes a charge-coupled device (CCD), referencenumeral 102 denotes a correlated double sampling circuit (CDS), andreference numeral 103 denotes a clamping circuit (CLP). Further,reference numeral 104 denotes an analog-digital converter (A/D),reference numeral 105 denotes frame memory, reference numeral 106denotes a zoom controller, reference numeral 108 denotes an imagecompensation unit, and reference numeral 107 denotes an image output.

In this mechanism, an optical image passes through the lens 100 and isformed on a photo-sensing surface of the CCD 101, which is an imagesensing device. The optical image formed on the photo-sensing surface ofthe CCD 101 is converted into photo-charges in a two-dimensionallyarranged photoelectric converter and sequentially transferred to theoutput. The correlated double sampling circuit 102 eliminates aCCD-specific reset noise from the output signals of the CCD 101 togenerate sampled-and-held video signals that are reset noise free.

The clamping circuit 103 performs clamping at the dark level, and the ADconverter 104 converts the input analog signals into digital signals.The frame memory 105 is memory for recording data on all pixels of oneframe. The zoom controller 106 reads out only a partial area around thecenter of the CCD when, for example, 2× zoomed image data is desired.

Recently, CMOS image sensors have been increasingly in use because theyare inexpensive, require no complicated timing generation circuits, andoperate with a single power supply while consuming less power.Furthermore, the CMOS image sensors have a characteristic which CCDimage sensors do not have, i.e., the ability of capturing only arbitraryareas of the CMOS image sensors as an image.

Description will be given of a high image quality electronic zooming ofa CMOS image sensor capable of reading out arbitrary areas (see JapanesePatent Laid-Open No. 2001-78081). FIG. 2 is a conceptual view ofelectronic zoom operations for CMOS image sensors. Reference numeral 201in FIG. 2 denotes readout method in normal mode, and reference numeral202 in FIG. 2 denotes readout method in zoom mode. In normal mode, forexample, a value obtained by adding together four pixel values of asolid image sensing device is read out as a pixel value for one pixel.In the range inside a bold line of 201, pixel values for shaded pixelsare read out, wherein each pixel value is obtained by adding togetherfour pixel values of that pixel and pixels at the right, lower right,and directly below that pixel. That is, pixel values for 4×4 pixels areread out from the range of 8×8 pixels.

On the other hand, in zoom mode, pixel values of an area of continuous4×4 pixels (a shaded part) around the center of the range of 8×8 pixelsinside the bold line are directly read out without addition. Then, thecenter portion in the bold line can be displayed in an enlarged form. Inaddition, since the number of read-out pixels is the same as that innormal mode and no pixel padding by signal processing is required, highimage quality can be provided in electronic zooming.

When photo-charges are accumulated in a CMOS sensor capable of blockreadout, the timing of starting the accumulation is controlled on a linebasis. Therefore, the time of accumulating the photo-charges does notalign between the lines. This temporal misalignment between the linescorresponds to the time required to read out one line. This timerequired to read out one line may be calculated by the followingequation.

The readout time per line=HBLK×α+Skip×β+the number of horizontal pixels×reference clocktime  Equation (1)

(α and β are values determined by the manner of addition in the verticaldirection.)

As an example, FIGS. 3A to 3C show driving that involves adding togetherand averaging two pixel lines in the vertical direction, where α is 2and β is 1. That is, the readout period per line is determined bysumming the following: time HBLK required to transfer the first line,time Skip required to skip the second line, time HBLK required totransfer the third line, and the time required to transfer pixel valuesin the horizontal direction obtained by adding together and averagingthe first and third lines.

The time required to transfer the pixel values in the horizontaldirection also depends on the reference clock time (the drivefrequency). That is, the readout period per line varies with the mannerof addition in the vertical direction and the drive frequency. As aresult, the misalignment of the time to start accumulation between thetop and bottom of a screen varies with changes in these drive modeconditions.

FIGS. 4A and 4B are diagrams for describing the misalignment of theaccumulation period according to the readout period per line. ComparingFIGS. 4A and 4B, the readout period per line in FIG. 4B is longer.Herein, the driving as in FIG. 4A with the shorter readout period perline will be referred to as a “drive mode A”, and the driving as in FIG.4B with the longer readout period per line will be referred to as a“drive mode B.” In drive mode A, the misalignment of the accumulationperiod between the top and bottom of the same display screen is smallerthan that in drive mode B.

Referring to FIG. 5, description will be given of the case where thedrive mode is switched in taking moving images, using EVF (ElectronicView Finder) and so forth. In FIG. 5, reference numeral 501 denotes thesum of the accumulation period and the readout period for pixel valuesin a frame driven in drive mode A. In FIG. 5, for lines for whichreadout for one frame has finished, accumulation of photo-charges forthe following frame is started. Therefore, the readout period for thepreceding frame overlaps the start of accumulation for the followingframe. Reference numeral 502 denotes the sum of the accumulation periodand the readout period when the drive mode is switched from drive mode Ato drive mode B at time t1. The switching of the drive mode is performedduring the VBLK (vertical blanking) period after the pixel values in theframe 2 are read out. That is, the accumulation start timingcorresponding to drive mode A is set for lines before the drive modeswitching, and the accumulation start timing corresponding to drive modeB is set for lines after the drive mode switching.

In the example shown in FIG. 5, the driving is performed in drive mode Abefore time t1, at which point the driving is switched to drive mode B.Since the reset starting time for the frame 3 is before time t1, thegradient due to the misalignment of the accumulation start timing in theperiod before time t1 corresponds to drive mode A. However, the drivemode is switched to drive mode B at time t1, so that the readout periodbecomes longer in contrast to drive mode A. As a result, themisalignment of the reset start timing for lines for which the reset isstarted after time t1 corresponds to drive mode B, causing a differentgradient of misalignment. Then, trying to maintain the frame rate wouldcause a difference in the accumulation period between the top and bottomof the same display screen for the frame 3.

Thus, as in the above example, when the readout period for a frameoverlaps the accumulation period for the following frame, switching thedrive mode causes a difference in the accumulation period in thefollowing frame, thereby reducing the quality of the output image.

SUMMARY OF THE INVENTION

According to one aspect of embodiments of the present invention relatesto an image sensing apparatus comprising, an image sensing unit adaptedto generate image data in which a plurality of lines are arranged, eachline having a plurality of pixel circuits each including alight-receiving unit which generates and accumulates charges accordingto a quantity of incident light, a reset unit adapted to execute a firstreset mode and a second reset mode on a frame basis, wherein the resetunit sequentially resets the light-receiving units at first timeintervals for every predetermined line in the first reset mode, andsequentially resets the light-receiving units at second time intervalsdifferent from the first time intervals for every predetermined line inthe second reset mode, and a readout unit adapted to execute a firstreadout mode and a second readout mode on a frame basis, wherein in thefirst readout mode, the readout unit reads out as pixel values thecharges accumulated in the light-receiving units at the first timeintervals for every the predetermined line after a predetermined timefrom start of the reset in the first reset mode, and in the secondreadout mode, the readout unit reads out as pixel values the chargesaccumulated in the light-receiving units at the second time intervalsfor every the predetermined line after a predetermined time from startof the reset in the second reset mode, and wherein, the reset unitperforms reset for a frame by the reset mode different from the resetmode of the preceding frame after completion of the readout of pixelvalues in the preceding frame by the readout unit.

According to another aspect of embodiments of the present inventionrelates to an image sensing apparatus comprising, an image sensing unitadapted to generate image data in which a plurality of lines arearranged, each line having a plurality of pixel circuits each includinga light-receiving unit which generates and accumulates charges accordingto a quantity of incident light, a reset unit adapted to sequentiallyreset the light-receiving units for every predetermined line, and areadout unit adapted to read out as pixel values the charges accumulatedin the light-receiving units for every the predetermined line after apredetermined time from start of the reset, wherein on a basis of framesof the image data, the readout unit reads out the pixel values afteradding the pixel values together when performing readout for a firstarea of the image sensing unit, and reads out the pixel values afteradding the pixel values together for smaller number of pixels than inthe readout for the first area or without addition when performingreadout for a second area smaller than the first area, and wherein, thereset unit executes, on a frame basis, a reset mode for sequentiallyresetting at first time intervals for every predetermined line beforereadout is performed for the first area, and a reset mode forsequentially resetting at second time intervals different from the firsttime intervals for every predetermined line before readout is performedfor the second area, the readout unit performs readout for the firstarea at the first time intervals for every the predetermined line andperforms readout for the second area at the second time intervals forevery the predetermined line, and the reset unit performs reset for aframe by the reset mode different from the reset mode of the precedingframe after completion of the readout of pixel values in the precedingframe by the readout unit.

According to further aspect of embodiments of the present inventionrelates to a method of controlling an image sensing apparatuscomprising: an image sensing unit adapted to generate image data inwhich a plurality of lines are arranged, each line having a plurality ofpixel circuits each including a light-receiving unit which generates andaccumulates charges according to a quantity of incident light; and areset unit adapted to execute a first reset mode and a second reset modeon a frame basis, wherein the reset unit sequentially resets thelight-receiving units at first time intervals for every predeterminedline in the first reset mode, and sequentially resets thelight-receiving units at second time intervals different from the firsttime intervals for every predetermined line in the second reset mode,the method comprising, a readout step of executing a first readout modeand a second readout mode on a frame basis, wherein in the first readoutmode, the charges accumulated in the light-receiving units are read outas pixel values at the first time intervals for every the predeterminedline after a predetermined time from start of the reset in the firstreset mode, and in the second readout mode, the charges accumulated inthe light-receiving units are read out as pixel values at the secondtime intervals for every the predetermined line after a predeterminedtime from start of the reset in the second reset mode, and a reset stepof the reset unit performing reset for a frame after completion of thereadout of pixel values in the preceding frame in the readout step.

According to one aspect of embodiments of the present invention relatesto a method of controlling an image sensing apparatus comprising: animage sensing unit adapted to generate image data in which a pluralityof lines are arranged, each line having a plurality of pixel circuitseach including a light-receiving unit which generates and accumulatescharges according to a quantity of incident light; and a reset unitadapted to sequentially reset the light-receiving units for everypredetermined line, the method comprising, a readout step of a readoutunit reading out as pixel values the charges accumulated in thelight-receiving units for every the predetermined line after apredetermined time from start of the reset, wherein, on a basis offrames of the image data, the pixel values are read out after adding thepixel values together when readout is performed for a first area of theimage sensing unit, and the pixel values are read out after addingsmaller number of pixel values together than in the readout for thefirst area or without addition when readout is performed for a secondarea smaller than the first area, and wherein, the readout for the firstarea is performed at first time intervals for every the predeterminedline and the readout for the second area is performed at second timeintervals different from the first time intervals for every thepredetermined line, and a reset step of the reset unit performing resetfor a frame by a reset mode different from a reset mode of the precedingframe after completion of the readout of pixel values in the precedingframe by the readout unit, wherein, in the reset step, on a frame basis,a reset mode for sequentially resetting at the first time intervals forevery predetermined line is performed before readout is performed forthe first area, and a reset mode for sequentially resetting at thesecond time intervals for every predetermined line is performed beforereadout is performed for the second area.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments (with reference to theattached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an exemplary mechanism for electroniczoom processing using a CCD;

FIG. 2 is a diagram for describing the concept of high image qualityelectronic zooming using partial readout;

FIGS. 3A, 3B, and 3C are diagrams for describing the concept of adifference in the accumulation period per line in adding together andaveraging two pixel lines in the vertical direction;

FIGS. 4A and 4B are diagrams for describing a change in the readoutperiod per line when the drive mode is switched;

FIG. 5 is a diagram for describing the misalignment of the accumulationperiod between the top and bottom of the same screen caused by switchingof the drive mode;

FIG. 6 is a diagram showing an exemplary configuration of an imagesensing apparatus according to embodiments of the present invention;

FIG. 7 is a diagram showing an exemplary configuration of a single pixelcircuit according to the embodiments of the present invention;

FIG. 8 is a diagram showing an exemplary configuration of pixel circuitsand readout circuits according to the embodiments of the presentinvention;

FIG. 9 is a diagram for describing readout timing according to a firstembodiment of the present invention;

FIGS. 10A and 10B are diagrams for describing a reduction in theaccumulation period according to the embodiments of the presentinvention;

FIG. 11 is a diagram for describing readout timing according to a secondembodiment of the present invention;

FIG. 12 is a diagram for describing readout timing according to a thirdembodiment of the present invention;

FIG. 13 is a diagram for describing a difference of image sensing areasfrom which pixel values are read out in a drive mode A and a drive modeB in the embodiments of the present invention;

FIG. 14 is a diagram showing an exemplary mechanism for reading outpixel values in a partial area of the image sensing area according tothe embodiments of the present invention;

FIG. 15 is a diagram showing an exemplary configuration of a horizontaldecoder unit 1406 and a horizontal shift register unit 1407 according tothe embodiments of the present invention; and

FIG. 16 is an exemplary timing chart of control signals according to theembodiments of the present invention.

DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present invention will be described in detail withreference to the drawings.

First Embodiment

FIG. 6 is a diagram showing an exemplary configuration of an imagesensing apparatus according to the embodiments.

In the image sensing apparatus in FIG. 6, a light from an object passesthrough an aperture blade 1 and is image-formed on an image sensingdevice 4 by a lens 2. Thus, photoelectric conversion is performed. Afilter group 3 is a combination of an optical low-pass filter forcutting off higher frequencies of the light to prevent moiré, a colorcompensation filter, a filter for cutting off infrared, and so forth.

The signals obtained by the conversion in the image sensing device 4have their pixel locations selected two-dimensionally by an X addressselecting unit 6 and a Y address selecting unit 5 with signals from anaddressing unit 8. The locations are read out to a timing adjusting unit7. The timing adjusting unit 7 adjusts the timing of the outputs (one ormore outputs) from the image sensing device 4.

The signals output from the timing adjusting unit 7 have their voltagecontrolled by an AGC (Auto Gain Control) 10 and are converted intodigital signals in an A/D converter 11. A camera DSP 12 performs imageprocessing for moving images or still images. An MPU 14 performsoperations such as setting parameters used in this image processing forthe camera DSP 12, performing AE and AF processing, and so forth.

The AF control is performed by a focus motor 51 moving a focus lens (notshown) back and forth. An oscillator 9 provides a clock pulse to theCamera DSP 12 and MPU 14. A display area specifying unit 19 acceptsspecification of the display area from a user of image sensingapparatus. The display area specifying unit 19 may be implemented as azoom button. DRAM 13 is used as a temporary storage area in the imageprocessing, and an image recording medium 18 is used as a nonvolatilestorage area. For example, the image recording medium 18 may be a smartmedium, a magnetic tape, or an optical disk. A video encoder 15, a CRT16, and so forth are provided for display after the image processing.

A viewfinder 17 may be an LCD or the like, for example, and is used forpurposes such as checking an object before storing it on the imagerecording medium 18. The output units are not limited to the CRT 16 andthe viewfinder 17 but may be implemented by using a printer and soforth.

The image sensing device 4 according to the embodiments comprises singlepixel circuits and readout circuits. First, the configuration andoperations of a single pixel circuit will be described with reference toFIG. 7.

In FIG. 7, a MOS transistor 158 is a transfer gate for controlling apotential barrier, which is used for transferring a charge accumulatedin a photodiode (referred to as a PD hereafter) 150 to a floatingdiffusion (referred to as an FD hereafter) configured to float a gate ofamplification MOS transistor 160.

A reset MOS transistor 157 is a transistor for resetting the charge ofthe PD 150. A MOS transistor 159 is provided for line selection. A gateof the MOS transistor 158 is connected to a transfer signal line 153 fortransferring the charge of the PD 150. A gate of the reset MOStransistor 157 is connected to a reset signal line 156 for resetting theFD. A gate of the MOS transistor 159 is connected to a select signalline 152.

The charge accumulated in the PD 150 is first transferred to the FD viathe MOS transistor 158 selected by the transfer signal line 153, whereinthe FD has been reset by the reset transistor 157 turned on by the resetsignal line 156. Then, the charge is amplified at the source followerMOS transistor 160 when the MOS transistor 159 is selected by the selectsignal line 152, and the charge is read out to a readout line 154.

In the embodiments, when an electronic zoom operation is performed usingan image sensing area comprising a set of single pixel circuits asabove, pixels included in a partial area within the image sensing areaare read out one by one in zoom mode (tele) without addition of pixelvalues. Alternatively, pixel values of a smaller number of pixels areadded together than in normal mode (wide) to be described later. Forexample, if an image sensing area 1301 shown in FIG. 13 represents theentire area that the image sensing device 4 can image, pixels includedin an area 1302 within the area 1301 are read out in zoom mode. Such adriving is referred to as “drive mode A” in the embodiments. On theother hand, in normal mode (wide), pixel values obtained by adding apredetermined number of pixels (e.g., 2×2=4 pixels) together are readout for the entire image sensing area 1301. Such a driving is referredto as “drive mode B” in the embodiments.

The number of pixels added together in drive mode B is not limited totwo lines (four pixels) but may be four lines (16 pixels). In that case,drive mode A may involve addition of two lines (four pixels) rather thanno addition.

If readout without addition is performed in drive mode A, a singlehorizontal period (a horizontal period A) corresponds to the period ofstoring pixel values for one line in the area 1302 into storagecapacitors in the readout circuits and then reading out the pixel valuesfrom horizontal output lines without addition. On the other hand, indrive mode B, image pixels for two lines are sequentially stored instorage capacitors in the readout circuits, and then added together andread out from the horizontal output lines. Therefore, a singlehorizontal period (a horizontal period B) corresponds to the period upto reading out the pixel values added together. That is, the horizontalperiod A is shorter than the horizontal period B.

With reference to FIG. 8, description will be given of a circuitconfiguration including a pixel section 801 in which a plurality ofsingle pixel circuits shown in FIG. 7 are arranged, and readout circuits802. For simplicity, only 2×2 pixels are shown in FIG. 8.

First, when pixel values are not added together in drive mode A (controlwithout addition), a MOS transistor 161-1 shown in FIG. 8 is activatedby a signal line 169. This causes a charge of a PD 150-1 to beaccumulated in a capacitor 162-1. Similarly, a charge of a PD 150-2 isread out to a capacitor 164-1 as readout of the PD 150-1 is controlledby signal lines 156-1, 153-1, 152-1, and 169. Then, signal lines 167-1and 167-2 are alternately turned on, so that the image signals from thePDs 150-1 and 150-2 are sequentially read out via an amplifier 171.Operations in the vertical direction are performed in a manner similarto the above under the control of 156-2, 153-2, and 152-2.

When pixel values are added together in drive mode B (control withaddition), charges of the PDs 150-1 and 150-2 are accumulated in thecapacitors 162-1 and 164-1 respectively, under the control of the signallines 156-1, 153-1, 152-1, and 169 shown in FIG. 8. Then, charges of PDs150-3 and 150-4 are accumulated in capacitors 162-2 and 164-2respectively, under the control of the signal lines 156-2, 153-2, 152-2,and 170. Thereafter, the signal lines 167-1 and 167-2 are simultaneouslyturning on, so that an image signal obtained by adding the charges fromthe PDs 150-1 to 150-4 together is read out via the amplifier 171.

In this manner, operations in drive mode A and drive mode B can beperformed.

In drive mode A, the partial area 1302 in the image sensing area 1301 isselected to read out pixel values therefrom. A mechanism for selectingthis partial area will be described with reference to FIG. 14.

FIG. 14 is a diagram showing a more detailed configuration of the imagesensing device 4, the Y address selecting unit 5, and the X addressselecting unit 6 according to this embodiment.

In FIG. 14, the image sensing device 4 includes an image sensing area1401 comprising 8×8 pixels, as well as readout circuits 1403corresponding to eight pixels in the horizontal direction. An imagesensing area 1402 is an area of 4×4 pixels in the image sensing area1401. In drive mode A, pixel values in the image sensing area 1402 areread out without addition. On the other hand, in drive mode B, pixelvalues in the image sensing area 1401 are added together and read out.It is assumed that addition of 2×2 pixels is employed here.

The Y address selecting unit 5 comprises a vertical decoder unit 1404and a vertical shift register unit 1405, whereas the X address selectingunit 6 comprises a horizontal decoder unit 1406 and a horizontal shiftregister unit 1407. The vertical decoder unit 1404 receives inputs ofVD0 to VD1, and the vertical shift register unit 1405 is adapted toreceive inputs of a clock pulse (CLK) and a vertical reset pulse (VRES).The vertical shift register unit 1405 outputs select signals 152,transfer signals 153, and reset signals 156. Similarly, the horizontaldecoder unit 1406 receives inputs of HD0 to HD1, and the horizontalshift register unit 1407 receives inputs of a clock pulse (CLK) and ahorizontal reset pulse (HRES).

The vertical decoder unit 1404 and the horizontal decoder unit 1406 areused to determine which of the entire image sensing area 1401 or thepartial image sensing area 1402 is selected. Since the Y addressselecting unit 5 and the X address selecting unit 6 operate in almostthe same manner in selection of the image sensing area, only selectionin the horizontal direction regarding the X address selecting unit 6will be described below.

FIG. 15 shows an exemplary configuration of the horizontal decoder unit1406 and the horizontal shift register unit 1407.

The inputs HD0 to HD1 of the horizontal decoder unit 1406 correspond totwo lines (bits). The image sensing area 1401 is divided into threeparts of two pixels, four pixels, and two pixels in the horizontaldirection. Therefore, the four pixels in the middle may be selected inorder to select the image sensing area 1402. As combinations of (HD0,HD1), for example, (0, 0) may correspond to selecting the first twopixels, (0, 1) may correspond to selecting the next four pixels, and (1,0) may correspond to selecting the last two pixels.

The horizontal shift register unit 1407, located in between thehorizontal decoder unit 1406 and the image sensing area 1401, shifts asignal obtained from the horizontal decoder unit 1406 with the clockpulse CLK. Simultaneously, the horizontal shift register unit 1407outputs a signal 167 to a readout circuit 1403, for reading out a pixelvalue from a pixel circuit in the image area 1401 via the horizontaloutput line. To stop driving of the horizontal shift register unit 1407,a signal pulse shifted by the horizontal shift register unit 1407 may beerased using the horizontal reset pulse HRES.

In FIG. 15, the horizontal decoder unit 1406 has inputs of HD0 for thelower digit and HD1 for the higher digit, and comprises inverters 1501and 1502 and AND circuits 1503 and 1504. The horizontal shift registerunit 1407 comprises D flip-flops 1505-1 to 1505-5 and OR circuits 1506-1and 1506-2. It is noted that the FIG. 15 is illustrated as a simplifiedview for describing the case where the four pixels corresponding to theimage sensing area 1402 are selected out of the eight pixels in thehorizontal direction. Therefore, the flip-flops illustrated in thehorizontal shift register unit 1407 are only part of actually arrangedflip-flops for the eight pixels.

Besides the configuration shown in FIG. 15, the circuit of thehorizontal decoder unit 1406 may be implemented by using devices otherthan AND devices and inverters, and the horizontal shift register unit1407 may be implemented by a clocked inverter as in conventional cases.

When (0, 1) is input to the inputs for (HD0, HD1) of the horizontaldecoder unit 1406, a signal 167 is output to the readout circuit 1403for the leftmost pixel among the four pixels in the image sensing area1402. Simultaneously, the flip-flop 1505-1 (FF1) is selected. Then, theclock pulse CLK causes sequential shifting to the FF2 (1505-2), FF3(1505-3), and FF4 (1505-4) for every clock. The output of the FF4(1505-4) is input to the FF5 (1505-5) via the OR circuit 1506-2.Therefore, when only the four pixels corresponding to the image sensingarea 1402 are selected, the reset pulse HRES may be input rather thaninputting (1, 0) for (HD0, HD1) to the AND circuit 1504. To furtherselect the two pixels following these four pixels, (1, 0) may be inputfor (HD0, HD1) so that the output of the AND circuit 1504 becomes 1.

By driving the vertical decoder unit 1404 and the vertical shiftregister unit 1405 in a similar manner, the 4×4 pixel area 1402 in theimage sensing area 1401 can be selected.

In this manner, only a partial image sensing area can be selected in theentire image sensing area.

FIG. 16 shows a timing chart of the control signals according to FIG.14. Reference numeral 1601 denotes the readout period in drive mode B,whereas reference numeral 1602 denotes the readout period in drive modeA.

Reference numeral 1603 denotes a single horizontal period in drive modeB. This is the time required to read out pixel values with a pair ofselect signals, for example 152-1 and 152-2, and then add these pixelvalues together to read out from the horizontal output line. Referencenumeral 1604 denotes a single horizontal period in drive mode A. This isthe time required to read out a pixel value with a single select signalline, for example 152-3, and then read out the pixel value from thehorizontal output line. The single horizontal period 1603 is longer thanthe single horizontal period 1604. In addition, the readout periods 1601and 1602 are defined as a set of such single horizontal periods 1603 and1604 respectively. Therefore, if the same number of pixels are read outfrom the horizontal output line as shown in FIG. 16, the readout period1601 is longer than the readout period 1602.

Next, the control over the switching of the drive mode in an embodimentwill be described. In this embodiment, the drive mode is switched afterreadout for one frame is completed, and the reset operation for thefollowing frame is started. In this manner, the reset operation for thefollowing frame will not be performed during the readout period for thepreceding frame. Therefore, the accumulation period for the followingframe can be made consistent in that frame. A conceptual view about thiswill be further described with reference to FIG. 9.

In FIG. 9, reference numerals 901 to 903 denote the sum of theaccumulation period and the readout period for frames 1 to 3respectively. The frame 1 (901) and the frame 2 (902) are driven indrive mode A. On the other hand, the frame 3 (903) is driven in drivemode B. The frame 1 (901) and the frame 2 (902) do not overlap eachother in their readout period and the accumulation period, so that oncethe readout period for the frame 1 (901) is completed at time t1, theaccumulation period for the frame 2 (902) is started. That is, thesignal lines 156 and 153 are turned on to reset the PD 150. In FIG. 9,switching from drive mode A to drive mode B is performed at time t2.Time t2 is the point where the readout of pixels of all lines in theframe 2 (902) is completed. Also, the accumulation period for the frame3 (903) is started at time t2.

In this manner, after the readout of pixels in a frame is completed, theaccumulation period for the following frame is started. This allows aconsistent accumulation period in that frame even when the drive mode isswitched.

However, due to the fact that the accumulation period for the followingframe cannot be started until the readout for the preceding frame iscompleted, the accumulation period naturally becomes shorter than in thecase where the readout period overlap the accumulation period betweentwo successive frames, if the frame rate is the same.

For example, in the case of FIG. 10A, accumulation for the followingframe is started during the readout period for the preceding frame. Theaccumulation period 1001 indicates the accumulation period given to thepixels in this case. On the other hand, in the case of FIG. 10B,accumulation for the following frame is started after the readout periodfor the preceding frame ends. The accumulation period 1002 indicates theaccumulation period given to the pixels in this case. The single frameperiod 1003 determining the frame rate is the same in both FIG. 10A andFIG. 10B.

Comparing the accumulation period 1001 and the accumulation period 1002,it can be seen that 1001>1002. Therefore, when the approach of FIG. 10Baccording to the present invention is employed, increasing the gain ofoutput pixel values is required.

Specifically, in this embodiment, the short accumulation period can becompensated by gain correction with a certain value for each line in theframes using the AGC 10. Furthermore, this embodiment is characterizedin that setting values for signal processing of frames are changed inthe DSP 12 after the drive mode switching. This is because, for example,a setting value for the edge enhancement needs to be changed to theoptimal value on each switching of the drive mode, since changes in theaddition and skipping of pixels caused by the drive mode switchingresult in the change in the resolution.

It is possible to shorten the time required to read out one line asdescribed above by increasing the driving frequency, and to extend theaccumulation period as a result. This improves the readout rate of theCMOS sensor and also solves the problem of the reduced accumulationperiod, thereby allowing obtaining a normal output without performingthe gain correction.

Thus, in this embodiment, the accumulation period for the followingframe is started after the readout for the preceding frame is completed.Therefore, even when the drive mode is switched between frames, it ispossible to avoid the situation in which the accumulation period becomesinconsistent in the frame immediately after the switching. In addition,for frames with the reduced accumulation period, a gain can be appliedto each line to compensate for the reduction.

Second Embodiment

In the first embodiment, for all frames, the timing of starting theaccumulation period for the following frame is set to after completionof the readout period. However, the adverse effect of the intensitydifference between the top and bottom of the display screen due to theoverlap of the readout period and the accumulation period is seen onlywhen the drive mode is switched. In addition, applying a gain to eachline in order to compensate for the accumulation period may cause anadverse effect that the S/N ratio deteriorates.

In the present embodiment, the following frame is reset after completionof the readout period only when the drive mode is switched. As a result,the decrease in the S/N ratio can be minimized because only a frame forwhich the drive mode is switched requires the increase of the gain.

For example, as shown in FIG. 11, a frame 1 and a frame 2 are in drivemode A, and the readout period for the frame 1 overlaps the accumulationperiod for the frame 2. If the drive mode is switched from A to B, thedrive mode is switched to B after the readout period is completed attime t1, and the accumulation period for a frame 3 is started.Thereafter, the readout period for the frame 3 and the accumulationperiod for a frame 4 are again set to overlap each other.

In this manner, it is possible to minimize the reduction in theaccumulation period by shifting the start of the accumulation period forthe following frame only when the drive mode is switched. In addition,the frame rate can be consistent irrespective of the drive modeswitching by adjusting the VBLK period for each frame. Furthermore, thisembodiment is characterized in that, as in the first embodiment, settingvalues for the signal processing of frames after the drive modeswitching are changed for smooth drive mode switching.

Third Embodiment

In the second embodiment, the frame rate is aligned by adjusting theaccumulation period so that the accumulation period for the frameimmediately after the drive mode switching becomes shorter than that forother frames. The present embodiment is characterized in that theaccumulation period is made equal to that for other frames by adjustingthe start time of readout for the frame immediately after the drive modeswitching.

For example, in FIG. 12, the drive mode is switched from A to B at timet1, so that the timing of reset and readout for the frame 3 andsubsequent frames is changed. In this embodiment, again, theaccumulation period for the frame 3 is started after completion of thereadout period for the frame 2. However, the readout is not starteduntil the accumulation period for the frame 3 becomes equal to that forother frames (the frame 4 and subsequent frames) in drive mode B.

As a result, the misalignment of the accumulation period as in thesecond embodiment does not occur. This eliminates the need to apply again in the vertical direction on the display screen and preventsdeterioration of the S/N ratio. Furthermore, as in the first embodiment,the setting values for signal processing of frames after the drive modeswitching can be changed for smooth drive mode switching.

The above description has been given for the cases where electroniczooming is performed. That is, it has been described that, in zoom mode(tele), pixel values of pixels included in a partial area of an imagesensing area are read out one by one without addition. In normal mode(wide), pixel values obtained by adding together a predetermined numberof pixels (e.g., 2×2=4 pixels) are read out for the entire image sensingarea 1301.

However, besides the above cases, the following case is also applicable.

When frame images are sequentially being read out, the followingprocessing may be performed for saving power consumption. That is, frameimages are sequentially reset at first time intervals for everypredetermined line up to a certain frame image. The charges accumulatedin the PDs are read out as pixel values at the first time intervals forevery said predetermined line. Then, the drive mode is switched, so thatsubsequent frame images are sequentially reset at second time intervalsdifferent from the first time intervals for every predetermined line.The charges accumulated in the PDs are read out as pixel values at thesecond time intervals for every said predetermined line.

The approaches of the first to third embodiments may be applied to theabove technique. This avoids the situation in which, even when the drivemode is switched between frames, the accumulation period is madeinconsistent in the frame immediately after the switching.

Other Embodiment

The object of the invention is also achieved by providing a system witha storage medium containing a program code of software for implementingthe above-described functions so that the system reads and executes theprogram code. In that case, the program code itself read from thestorage medium implements the functions of the above-describedembodiments, and the storage medium containing the program code isincluded in the present invention. The present invention also covers thecase where an operating system (OS) or the like operating on a computerunder instructions of the program code performs part or all of actualprocessing by which the above-described functions are implemented.

The present invention may also be implemented in a manner in which theprogram code read from the storage medium is written to memory providedin a function extension card inserted into a computer or a functionextension unit connected to a computer. Under instructions of theprogram code, a CPU or the like in the function extension card or thefunction extension unit performs part or all of actual processing toimplement the above-described functions.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2005-255616, filed Sep. 2, 2005, which is hereby incorporated byreference herein in its entirety.

1. An image sensing apparatus comprising: an image sensing unit adaptedto generate image data in which a plurality of lines are arranged, eachline having a plurality of pixel circuits each including alight-receiving unit which generates and accumulates charges accordingto a quantity of incident light; a reset unit adapted to execute a firstreset mode and a second reset mode on a frame basis, wherein the resetunit sequentially resets the light-receiving units at first timeintervals for every predetermined line in the first reset mode, andsequentially resets the light-receiving units at second time intervalsdifferent from the first time intervals for every predetermined line inthe second reset mode; and a readout unit adapted to execute a firstreadout mode and a second readout mode on a frame basis, wherein in thefirst readout mode, the readout unit reads out as pixel values thecharges accumulated in the light-receiving units at the first timeintervals for every said predetermined line after a predetermined timefrom start of the reset in the first reset mode, and in the secondreadout mode, the readout unit reads out as pixel values the chargesaccumulated in the light-receiving units at the second time intervalsfor every said predetermined line after a predetermined time from startof the reset in the second reset mode, and wherein, the reset unitperforms reset for a frame by the reset mode different from the resetmode of the preceding frame after completion of the readout of pixelvalues in the preceding frame by the readout unit.
 2. An image sensingapparatus comprising: an image sensing unit adapted to generate imagedata in which a plurality of lines are arranged, each line having aplurality of pixel circuits each including a light-receiving unit whichgenerates and accumulates charges according to a quantity of incidentlight; a reset unit adapted to sequentially reset the light-receivingunits for every predetermined line; and a readout unit adapted to readout as pixel values the charges accumulated in the light-receiving unitsfor every said predetermined line after a predetermined time from startof the reset, wherein on a basis of frames of the image data, thereadout unit reads out the pixel values after adding the pixel valuestogether when performing readout for a first area of the image sensingunit, and reads out the pixel values after adding the pixel valuestogether for smaller number of pixels than in the readout for the firstarea or without addition when performing readout for a second areasmaller than the first area, and wherein, the reset unit executes, on aframe basis, a reset mode for sequentially resetting at first timeintervals for every predetermined line before readout is performed forthe first area, and a reset mode for sequentially resetting at secondtime intervals different from the first time intervals for everypredetermined line before readout is performed for the second area, thereadout unit performs readout for the first area at the first timeintervals for every said predetermined line and performs readout for thesecond area at the second time intervals for every said predeterminedline, and the reset unit performs reset for a frame by the reset modedifferent from the reset mode of the preceding frame after completion ofthe readout of pixel values in the preceding frame by the readout unit.3. The image sensing apparatus according to claim 1, wherein, when thereadout unit performs readout by switching between two successive framesfrom readout at the first time intervals for every said predeterminedline to readout at the second time intervals for every saidpredetermined line, or from readout at the second time intervals forevery said predetermined line to readout at the first time intervals forevery said predetermined line, the reset unit performs reset for thefollowing frame after completion of readout of pixel values in thepreceding frame, and when the switching is not performed between the twosuccessive frames, the reset unit performs reset for the following framebefore completion of readout of pixel values in the preceding frame. 4.The image sensing apparatus according to claim 3, wherein, the readoutunit controls the time of starting readout in the following frame sothat the period from start of the reset to start of readout in thefollowing frame becomes equal to the period from start of the reset tostart of readout in frames subsequent to the following frame.
 5. Theimage sensing apparatus according to claim 3, further comprising a gaincorrection unit adapted to correct a gain of pixel values in thefollowing frame to compensate difference of accumulation period of thetwo successive frames when the switching is performed between the twosuccessive frames.
 6. The image sensing apparatus according to claim 1,comprising a signal processing unit adapted to process signals from theimage sensing unit, and a display unit adapted to display the signalsprocessed by the signal processing unit.
 7. A method of controlling animage sensing apparatus comprising: an image sensing unit adapted togenerate image data in which a plurality of lines are arranged, eachline having a plurality of pixel circuits each including alight-receiving unit which generates and accumulates charges accordingto a quantity of incident light; and a reset unit adapted to execute afirst reset mode and a second reset mode on a frame basis, wherein thereset unit sequentially resets the light-receiving units at first timeintervals for every predetermined line in the first reset mode, andsequentially resets the light-receiving units at second time intervalsdifferent from the first time intervals for every predetermined line inthe second reset mode, the method comprising: a readout step ofexecuting a first readout mode and a second readout mode on a framebasis, wherein in the first readout mode, the charges accumulated in thelight-receiving units are read out as pixel values at the first timeintervals for every said predetermined line after a predetermined timefrom start of the reset in the first reset mode, and in the secondreadout mode, the charges accumulated in the light-receiving units areread out as pixel values at the second time intervals for every saidpredetermined line after a predetermined time from start of the reset inthe second reset mode; and a reset step of the reset unit performingreset for a frame by the reset mode different from the reset mode of thepreceding frame after completion of the readout of pixel values in thepreceding frame in the readout step.
 8. A method of controlling an imagesensing apparatus comprising: an image sensing unit adapted to generateimage data in which a plurality of lines are arranged, each line havinga plurality of pixel circuits each including a light-receiving unitwhich generates and accumulates charges according to a quantity ofincident light; and a reset unit adapted to sequentially reset thelight-receiving units for every predetermined line, the methodcomprising: a readout step of a readout unit reading out as pixel valuesthe charges accumulated in the light-receiving units for every saidpredetermined line after a predetermined time from start of the reset,wherein, on a basis of frames of the image data, the pixel values areread out after adding the pixel values together when readout isperformed for a first area of the image sensing unit, and the pixelvalues are read out after adding smaller number of pixel values togetherthan in the readout for the first area or without addition when readoutis performed for a second area smaller than the first area, and wherein,the readout for the first area is performed at a first time intervalsfor every said predetermined line and the readout for the second area isperformed at a second time intervals different from the first timeintervals for every said predetermined line; and a reset step of thereset unit performing reset for a frame by a reset mode different from areset mode of the preceding frame after completion of the readout ofpixel values in the preceding frame by the readout unit, wherein, in thereset step, on a frame basis, a reset mode for sequentially resetting atthe first time intervals for every predetermined line is performedbefore readout is performed for the first area, and a reset mode forsequentially resetting at the second time intervals for everypredetermined line is performed before readout is performed for thesecond area.
 9. The method of controlling an image sensing apparatusaccording to claim 7, wherein, when readout is performed in the readoutstep by switching between two successive frames from readout at thefirst time intervals for every said predetermined line to readout at thesecond time intervals for every said predetermined line, or from readoutat the second time intervals for every said predetermined line toreadout at the first time intervals for every said predetermined line,reset for the following frame is performed in the reset step aftercompletion of readout of pixel values in the preceding frame, and whenthe switching is not performed between the two successive frames, resetfor the following frame is performed in the reset step before completionof readout of pixel values in the preceding frame.
 10. The method ofcontrolling an image sensing apparatus according to claim 9, wherein inthe readout step, the time of starting readout in the following frame iscontrolled so that the period from start of the reset to start ofreadout in the following frame becomes equal to the period from start ofthe reset to start of readout in frames subsequent to the followingframe.
 11. The method of controlling an image sensing apparatusaccording to claim 9, further comprising a gain correction step ofcorrecting a gain of pixel values in the following frame to compensatedifference of accumulation period of the two successive frames when theswitching is performed between the two successive frames.
 12. A computerstorage medium having a control program for image sensing apparatus whenexecuted by a computer to perform the method according to claim 7.